The migration of Σ3{112} incoherent twin boundary step in face-centered cubic metals under uniaxial loading

Abstract

Pure steps such as Σ3{112} incoherent twin boundary (ITB) steps often present along the coherent twin boundary regardless of deformation or annealing twins in metals with a face-centered cubic (FCC) structure. Corresponding to the defect structure of Σ3{112} ITB step, this pure step is composed of multiple Shockley partial dislocations with a net zero Burgers vector. It is generally believed that such pure steps do not move under mechanical loading because of the zero Peach–Koehler force. Here, we demonstrate the migration of pure steps by atomistic simulations under uniaxial tension and reveal the driving force associated with elastic anisotropy, i.e., the driving force originates from an imbalance in the elastic strain energy density across the TBs. Therefore, we introduce a compliance anisotropy factor, calculated by density functional theory, to characterize the migration capability of the Σ3{112} ITB step in FCC metals.